What happened
On January 18, 2013, a Cessna 152, registration PR-EJX, was conducting a flight training mission from Jundiaí (SBJD) to Piracicaba (SDPW). The crew, consisting of an instructor and a student, was performing a flight for the purpose of obtaining a Commercial Pilot License.
During the approach to runway 35 at the Piracicaba aerodrome, the aircraft experienced an engine failure. After attempts to restart the engine were unsuccessful, the crew initiated a left-hand pattern from an altitude of approximately 700 feet to perform a forced landing in a field of low vegetation. During the landing roll, the aircraft struck termite mounds, resulting in the nose gear collapsing and causing substantial damage to the aircraft. Both occupants sustained minor injuries.
The investigation
CENIPA investigators examined the Lycoming O-2/35-L2C engine and found that the failure was caused by the breakage of an intermediate crankshaft gear (P/N 75072) and specific mounting bolts (P/N LW-25-0.63). The investigation revealed that the failure originated from the excessive wear and subsequent breakage of the bolts securing the gear. The head of one broken bolt had become lodged between the gear teeth, leading to an overload condition that fractured the gear.
Investigators noted that the most probable cause for this wear was either the incorrect application of torque or a complete lack of torque during a previous maintenance procedure.